Studies are being carried out in animals with experimentally induced myocardial ischemia and hypoxia, to clarify relationships between mechanical and metabolic changes. In an isolated perfused rabbit heart system developed in our laboratory, we are examining 1) epicardial fluorescence and rates of lactate and pyruvate production as a technique for rapidly quantifying absolute or relative severity of ischemia; 2) contracture and compliance changes, especially in relationship to alterations in ultrastructure. These studies are intended to clarify basic mechanisms which may be applicable in the intact circulatory system. In intact animals, we are carrying out studies of 1) relationship between flow, function, and necrosis in the margins of experimentally produced infarcts in dogs; 2) mechanical effects of ischemia in central and border zone ischemic tissues, assessed by left ventricular wall thickness measurements made through echocardiographic scanning. These techniques may allow accurate computation of studies will lead to a better understanding of flow and performance characteristics of marginally ischemic myocardial tissues, and may aid in design of experiments to improve their salvage.